Chemical and electrochemical advanced oxidation processes as a polishing step for textile wastewater treatment: A study regarding the discharge into the environment and the reuse in the textile industry

Abstract

Abstract This study was focused on the application of various chemical and electrochemical advanced oxidation processes (AOPs/EAOPs) as a polishing step for the remediation of a textile wastewater, concerning its discharge into the environment and its reuse in the textile industry. The textile wastewater was previously subjected to biological treatment, clarification and filtration. The following processes were compared: hydrogen peroxide (H2O2) photolysis with ultraviolet C (UVC) radiation (H2O2/UVC), anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2) and AO-H2O2 with UVC radiation (AO-H2O2/UVC). Furthermore, the influence of H2O2 concentration on the H2O2/UVC process and the influence of current density on the AO-H2O2/UVC process were evaluated. The efficiency of the AOPs/EAOPs was assessed in terms of decolorization and mineralization. The decolorization ability of the various processes up to 25–30 min of reaction could be arranged in the following sequence: AO > AO-H2O2/UVC ≈ H2O2/UVC > AO-H2O2. For treatment times above 25–30 min, the AO-H2O2/UVC and H2O2/UVC processes provided higher decolorization than the AO process. Complete color removals were found, contrasting with a maximum mineralization of 39%, thereby indicating the presence of recalcitrant non-colored organic compounds. The German color discharge standards were achieved after 5–9 min of reaction for all processes, whereas the Brazilian color discharge limit was reached after 10 min of reaction for the AO process, 20 min for the AO-H2O2/UVC and H2O2/UVC processes, and 35 min for the AO-H2O2 process. The feasibility of using the recycled textile wastewater in textile processing was proved for scouring, bleaching and dyeing processes, taking into account hydrophilicity, color difference and whiteness index. The treatment times required for reuse purposes applying the H2O2/UVC process were equal or higher than the ones necessary for discharge purposes: 45 min for scouring, 20 min for bleaching, and 30 min for dyeing.